Others have told you how to access communities on other sites, so let’s focus on why it is this way.

Websites that use ActivityPub – that is, websites running things like Lemmy, Mastodon, PixelFed, PeerTube, BookWyrm, FunkWhale, and even some WordPress sites – are engaging in an auto-syndication or auto-mirroring system. If I have an account on lemmy.world (LW), I can post something to a community on lemm.ee (LE). That post will be sent by LW to LE, and then LE will send it out to every other website that is subscribed to that community. That means that you, here on lemmy.ca (LC) will be able to see it once LC receives it.

What you will be looking at, though, is a copy of the post on LE. And, indeed, what LE is hosting will actually be a copy of the post that originally got posted to LW. Everything’s happening locally here. We’re all interacting with local copies of material that is being syndicated to hundreds or thousands of other websites.

When you comment on my post, that comment first lives on lemmy.ca. LC will forward it along to lemm.ee, and then LE will distribute it to all of the other sites. That way, my account on lemmy.world can see that you said something.

This is all really neat, but sometimes it can seem too clever by half. For instance, these websites do not syndicate with every other Fediverse website in existence. It can’t. There’s no central directory of websites, there’s no phoning home, so one website cannot know about the existence of another unless someone goes out of their way to introduce them. If I were to start a new Lemmy-based website today – kichae.social – I would not be able to find any communities hosted on LC, LW, LE, or any others using the search feature. My website wouldn’t know they existed, and would not have a list of communities they host. Similarly, none of those website would know about mine, or any communities I’m hosting.

The network grows by direct, personal intervention by users. If I want to see !lemmy_ca_support@lemmy.ca on kichae.social, I need to copy the community’s URL and then paste that into kichae.social’s search bar. This will tell Lemmy to go and fetch whatever it finds at that address, assuming it’s a community or post. Once it’s done that, though, I can subscribe, and content will start to flow from LC to kichae.social.

Well, at least, content from this community. Syndication on Lemmy happens on a community-by-community basis.

Fediverse subscriptions also, generally, work the same way magazine subscriptions do. You don’t get the back catalogue once you’ve subscribed. It’s point-in-time-forward only. Some sites do pull in a sample of posts – I believe Lemmy-based sites work this way – but not all will.

On larger or more established sites like lemmy.ca, this isn’t really an issue. But if you find yourself wanting to run your own site, or think you’d prefer the experience on a smaller, niche fediverse site, it’s good to keep in mind. You should be able to access stuff from other websites, but you might have to put in more legwork in a more rarefied space.